Photolithography is a common technique used in the manufacture of semiconductor products. Photolithography processes involve the formation of features by using a photo-mask to expose certain regions of a photo-resist layer to light. The exposed or unexposed regions are then developed away to expose a semiconductor layer underneath the photo-resist. The exposed semiconductor layer can then have various processes performed thereon such as etching or doping.
A photo-mask typically includes a transparent layer with an opaque layer formed on top. Specific regions of the opaque layer are then removed to expose the transparent layer underneath. The transparent regions can thus allow light to travel through to expose specific regions of a photo-resist layer to light, typically an ultra-violet type of light.
Sometimes, however, errors occur during the formation of a mask. These errors should be repaired before the mask is used. There may be several regions of the mask which have to be repaired by etching away opaque regions where those regions are not wanted. It is sometimes better to perform these repairs individually rather than with a single etching process.